Controlling electrode-potential distribution to enable oxidation stability of MXene-based CDI desalination cells

MXenes, by virtue of good electron conductivity, rich surface functional groups, and reversible redox pseudocapacitance, have attracted enormous attention for capacitive deionization (CDI) towards the relief of global freshwater scarcity. However, the self-restacking of 2D MXene nanosheets, tortuous ion transport pathways, and inherent oxidation instability at anodic potentials severely hinder their practical application, particularly for using as a CDI anode. Herein, by coupling silver nanowires (AgNWs) with holey MXene layers (hMXene), we synthesized a freestanding Ag@hMXene anode and demonstrated its excellent anti-oxidation stability during CDI process owing to the depolarization effect of AgNWs. Benefiting from the in-plane pores across the hMXene basal plane and cross-linked AgNWs between hMXene sheets, Ag@hMXene exhibits a significantly improved specific surface area, ion transport kinetics and electrical conductivity. First-principle calculations demonstrated that the introduction of AgNWs effectively reduces the work function for the Ag@hMXene anode and inhibits the anodic polarization. As a result, the Ag@hMXene‖hMXene cell achieves a higher cell potential of 1.0 V compared to the MXene‖MXene cell (0.6 V), along with a 3-fold increase in both salt adsorption capacity and adsorption rate.